This invention relates to a circuit and method to reduce the effects of temperature on potentiometer based position sensors.
For devices which sense the position of a movable mechanical device or portion thereof, a potentiometer or variable resistor is often used. The wiper arm of the potentiometer is connected to the movable portion of the mechanical device such that motion of the device results in motion of the wiper arm. The changed resistance results in a signal which corresponds to the amount of motion of the mechanical device.
When this type of position sensor is employed in a high temperature environment, the potentiometer may exhibit a drop in resistance with increasing temperature. This change in resistance could be interpreted by the electronic monitor as a change in the position of the mechanical device. This false reading may result in an improper or untimely command being processed by the control circuitry.
The subject invention is designed to minimize the thermal effects on the position sensor. The scheme involves measuring the time needed for a comparator to change states given different input signals. The change-of-state time period under one input condition is divided by the time period under a second input condition. The quotient of the time periods is a function of resistance values which translates to a measure of the actuator's position. Both sides of the potentiometer are subject to the effects of temperature. These effects are cancelled out by taking the quotient of the time periods.